A 52-year-old male presents with acute-onset shoulder pain and weakness of external rotation following a fall on an outstretched hand. Examination reveals atrophy of the infraspinous fossa. All of the following nerves may be injured in this scenario EXCEPT:

Explanation

## Nerve Injuries in Shoulder Trauma — All EXCEPT **Key Point:** In traumatic shoulder injuries (FOOSH, anterior dislocation, proximal humerus fractures), the nerves most at risk are those anatomically close to the glenohumeral joint and axilla. The **radial nerve** is NOT primarily injured in this scenario. ### Clinical Presentation Analysis The patient presents with: - **Weakness of external rotation** → infraspinatus (suprascapular nerve) and/or teres minor (axillary nerve) involvement - **Infraspinous fossa atrophy** → confirms infraspinatus denervation → **suprascapular nerve** injury - **Mechanism:** FOOSH with likely anterior shoulder dislocation or proximal humerus fracture ### Nerves at Risk in Shoulder Trauma | Nerve | Course | Vulnerable in This Scenario? | Clinical Finding if Injured | | --- | --- | --- | --- | | **Suprascapular nerve** | Passes through suprascapular notch → innervates supraspinatus + infraspinatus | ✅ YES — traction, fracture fragments | Infraspinous fossa atrophy, weakness of abduction and **external rotation** | | **Axillary nerve** | Passes through quadrangular space → innervates deltoid + teres minor | ✅ YES — anterior dislocation, proximal humerus fracture | Deltoid atrophy, loss of abduction, sensory loss over lateral shoulder | | **Upper subscapular nerve** | Arises from posterior cord (C5–C6) → innervates upper subscapularis | ✅ YES — posterior cord injuries in brachial plexus traction from FOOSH | Loss of internal rotation (subscapularis) | | **Radial nerve** | Passes through **radial groove on mid-humeral shaft** | ❌ NOT in this scenario — injured in **mid-shaft humerus fractures**, not proximal/shoulder injuries | Wrist drop, loss of finger extension, sensory loss dorsal first web space | ### Why Radial Nerve Is the Exception **Clinical Pearl:** The **radial nerve** winds around the posterior aspect of the **mid-shaft of the humerus** in the radial (spiral) groove. It is classically injured in **mid-shaft humeral fractures** ("Holstein-Lewis fracture"), not in proximal humerus fractures or anterior shoulder dislocations. In the scenario described (FOOSH with infraspinous fossa atrophy and external rotation weakness), the injury is at the level of the shoulder/proximal humerus — the radial nerve is not in the path of injury at this level. In contrast: - **Suprascapular nerve** — passes through the suprascapular notch; vulnerable to traction and fracture fragments at the shoulder → explains infraspinous fossa atrophy - **Axillary nerve** — passes through the quadrangular space; most commonly injured nerve in anterior shoulder dislocation (5–10% of cases) - **Upper subscapular nerve** — arises from the posterior cord; can be injured in brachial plexus traction injuries associated with FOOSH **High-Yield (Gray's Anatomy / BD Chaurasia):** The radial nerve is at risk in **mid-shaft humerus fractures**, while the **axillary nerve** is at risk in **surgical neck fractures** and **anterior dislocations**. The **suprascapular nerve** is at risk in **suprascapular notch compression** and **proximal humerus fractures**. **Mnemonic:** **"Radial = mid-shaft; Axillary = surgical neck/dislocation; Suprascapular = notch/proximal fracture"** ### Summary The question asks which nerve is **NOT** injured in this shoulder trauma scenario. The **radial nerve** (Option A) is the correct exception because it is anatomically remote from the shoulder joint at the level of injury described, running in the radial groove of the mid-humeral shaft rather than near the glenohumeral joint or axilla.